Many automatic sliding doors are equipped with safety systems intended to detect potential interference with the closing operation of the doors. These safety systems usually include a plurality of signal sources, disposed on one door, and a plurality of receivers, disposed on the other door. The signal sources emit a curtain of signals across the threshold of the door to be detected by the plurality of receivers. When the signal curtain is interrupted, the safety system communicates with a door controller either to cease the closing operation and open the doors or to maintain the doors open, depending on the initial position of the doors.
A doorway safety system described in U.S. Pat. No. 4,029,176 to Gerald W. Mills and entitled "Doorway Safety Device" uses acoustic wave transmitters and receivers to detect endangered objects or persons. Not only does the patented system detects objects positioned between the doors and across the threshold, but it also extends the zone of detection into the entryway. The transmitters send out a signal at an angle into the entryway. When an obstruction enters the detection zone, the signal reflects from the obstruction and is detected by the receivers.
Similarly, a published European Patent Application No. EP 0699619A2 to Memco Limited and entitled "Lift Installation for Preventing Premature Closure of the Sliding Doors" describes a three-dimensional system for detecting objects or persons not only across the threshold, but also in the entryway.
For the three-dimensional detection system to work properly, the signal must be emitted into an entryway at a specific angle. Conventional technology uses optical devices that protrude from a circuit board. To obtain a particular angle, a lead of the optical device protruding from the circuit board must be bent. To ensure uniformity among multiple optical devices, a plastic holder is often used to maintain the optical device at a specific angle. This conventional approach is labor intensive and therefore, expensive. Additionally, the plastic holder has a certain thickness which results in a greater space requirement. Furthermore, the bent leads of the optical device typically cause reliability problems.
Modern surface mount technology is available and generally results in smaller packaging, less labor, and thus, lower cost. However, surface mount optical devices currently available, such as LEDs (light emitting devices) and photodiodes, typically do not include a lens. Also the existing surface mount technology does not include optical devices providing a signal at an angle.